The Drake equation is a mathematical formula for the probability of finding life or advanced civilization in the Universe.In 1961, the famous astronomer
Frank Drake proposed a formula, which became known as the "
Drake equation ". It uses several factors and tries to estimate the number of extraterrestrial intelligent civilizations that exist in our Galaxy at any moment [more precisely, the numbers of extraterrestrial civilizations in the Galaxy, with which humanity has a chance to make contact / approx. trans.]. Since its inception, several projects have been launched that are trying to find evidence of the existence of extraterrestrial civilizations, known collectively as “search for extraterrestrial intelligence” (search for extra-terrestial intelligence,
SETI ).
The most famous organization is the
SETI Institute , which for the last several decades has been engaged in combing space in search of radio waves with messages from extraterrestrial civilizations. But, according to a
new study , trying to clarify the Drake equation, conducted by an international team of astronomers, even if we discover extraterrestrial signals, the civilization that sent them by that time will be dead for a long time.
The study "
Coverage Area of Expanding Extraterrestrial Signals in the Galaxy: SETI and the Drake Equation " has recently become available online. The study was led by Claudio Grimaldi from the EPF-Lausanne Institute, together with Geoffrey Marcy (later professor) and Nathaniel Tellis (astronomer) from the University of California, Berkeley, and Francis Drake himself, who is now an assistant professor at SETI and the University of California at Santa Cruz.
Frank Drake writes his famous equation on the blackboard.Recall that the Drake equation postulates that the number of civilizations in our galaxy can be calculated by multiplying the average number of stars produced per year in our galaxy R, the proportion of sun-like stars with planets f
p , the average number of planets (and satellites) with suitable conditions for the origin civilization n
e , the probability of the birth of life on a planet with suitable conditions f
l , the probability of the occurrence of rational life forms on a planet on which there is life f
i , the ratio of the number of planets whose reasonable inhabitants are contact us and look for it, to the number of planets on which there is intelligent life f
c , the time during which civilization exists, is capable and wants to make contact L.
All this is written as N = R × f
p × n
e × f
l × f
i × f
c × L. The team began the study by making assumptions about the two key parameters of the equation. They suggested that civilizations appear in the Galaxy (N) at a constant speed, and that they will not emit electromagnetic waves (radio signals) forever, but will experience some time limit (L).
As Dr. Grimaldi explained to us:
We assume that a hypothetical civilization transmitting signals (emitters) transmits isotropic electromagnetic signals for a certain time L, and that the rate of nucleation of these radiations is constant. Each radiation process generates a spherical shell of thickness cL (where c is the speed of light), filled with electromagnetic waves. The outer radius of the spherical shell grows at the speed of light.
Panorama of the Milky Way at 360 °, composed of photos of ESO.
Simply put, they assumed that technological advanced civilizations are born and die in our Galaxy with a constant speed. However, they do not send signals at infinite speed — their transmissions will move at the speed of light, and they can be detected only in certain parts of space. The team then developed a model of the galaxy to determine whether humanity would have the chance to detect such signals.
The model assumed that the alien signals were shaped like a ring, gradually passing through our galaxy. As explained Grimaldi:
We modeled the galaxy as a disk. Emitters appear in random parts of the disk. Each spherical shell intersects with the disk in a ring. The probability that the ring will cross any point of the disk (for example, the Earth) is equal to the ratio of the area of the ring and the area of the disk. The total area of the ring on the galactic disk gives the average number of electromagnetic signals (N) crossing any chosen point (for example, the Earth). This average is key because SETI can detect signals only if they pass the Earth during their measurements.
As they determined from their calculations, two cases can be distinguished from this model, differing in whether the radiation envelope (1) is thinner than the size of the Milky Way or (2) thicker. This corresponds to the lifetime of technologically advanced civilizations (L), which may be more or less than the time it takes for the light to cross the Milky Way (about 100,000 years). As explained Grimaldi:
The average number (N) of signals passing by the Earth depends on the duration of the signal (L) and the rate of nucleation. N is obtained equal to L multiplied by the birth rate, which coincides with N from the Drake equation (the average number of civilizations emitting signals at the moment). The result is naturally obtained from our assumption that the rate of nucleation of signals is constant.
In the first case, the wall thickness of each shell will be less than the size of our Galaxy, and will fill only part of its volume (which will lower the probability of its detection using SETI). However, if the detected civilizations will arise quickly enough, these shells will be able to fill our Galaxy and even overlap each other. In the second case, each shell will be thicker than our Galaxy, which will increase the probability of detection using SETI.
Based on all this, the team also calculated that the average number of alien signals crossing the Earth’s position at any time would be equal to the number of civilizations transmitting signals at the moment. Unfortunately, they also determined that civilizations, the signals of which we will receive, will have died out by then. Therefore, in essence, the civilizations we heard will not be the ones that are still transmitting signals at the moment.
As Grimaldi explained, this raises interesting questions in connection with SETI research:
Instead of considering N Drake as the product of the probabilities of a civilization that transmits signals, our results suggest that N can be measured directly (at least in principle), since it coincides with the average number of signals crossing the Earth’s position.
This may disappoint people hoping to find evidence of the existence of extraterrestrial civilizations throughout their lives. On the one hand (depending on the number of civilizations existing in the Galaxy) we may have problems with receiving extraterrestrial transmissions. On the other hand, if we accept such a transmission, it may be that it will come from a long-vanished civilization.
SETI radio telescopes from the Allen Telescope Array (ATA) arrayIt also means that if a civilization can receive our radio signals, we will no longer be alive to meet them. However, this does not exclude the possibility that we will find evidence of the existence of intelligent life in our galaxy in the past. During its life, humanity may even find evidence of the existence of several alien intelligent civilizations. In addition, all these arguments do not reject the likelihood of finding an existing civilization.